Apparatus and method for measuring an induced perturbation to determine a physiological parameter

ABSTRACT

A monitor for determining a patient&#39;s physiological parameter includes a calibration device configured to provide a calibration signal representative of the patient&#39;s physiological parameter. An exciter is positioned over a blood vessel of the patient for inducing a transmitted exciter waveform into the patient. A noninvasive sensor is positioned over the blood vessel, where the noninvasive sensor is configured to sense a hemoparameter and to generate a noninvasive sensor signal representative of the hemoparameter containing a component of a physiological parameter waveform and a component of a received exciter waveform. In this context, a hemoparameter is defined as any physiological parameter related to vessel blood such as pressure, flow, volume, velocity, blood vessel wall motion, blood vessel wall position and other related parameters. A processor is configured to determine a relationship between a property of the received exciter waveform and a property of the physiological parameter. The processor is connected to receive the calibration signal and the noninvasive sensor signal, and the processor is configured to process the calibration signal and the noninvasive sensor signal to determine the physiological parameter. In the preferred embodiment, the physiological parameter measured is blood pressure, however, the present invention can also be used to analyze and track other physiological parameters such as vascular wall compliance, strength of ventricular contractions, vascular resistance, fluid volume, cardiac output, myocardial contractility and other related parameters.

RELATED APPLICATIONS

This application is a continuation in part of the following patentapplications and incorporates these applications by reference:

Caro, U.S. Ser. No. 08/228,213 filed on Apr. 15, 1994; and

Caro, Apparatus and Method for Measuring an Induced Perturbation toDetermine a Physiological Parameter, U.S. Provisional patent applicationSer. No. 60/005,179 filed on Oct. 3, 1995 (Atty Docket No. A-59155-1).

FIELD OF THE INVENTION

The present invention relates to an apparatus and method fornoninvasively providing a determination of a patient's physiologicalparameter and other clinically important parameters.

BACKGROUND OF THE INVENTION

Blood pressure is the force within the arterial system of an individualthat ensures the flow of blood and delivery of oxygen and nutrients tothe tissue. Prolonged reduction or loss of pressure severely limits theamount of tissue perfusion and could therefore result in damage to oreven death of the tissue. Although some tissues can toleratehypoperfusion for long periods of time, the brain, heart and kidneys arevery sensitive to a reduction in blood flow. Thus, during and aftersurgery, blood pressure is a frequently monitored vital sign. Bloodpressure is affected, during and after surgery, by the type of surgeryand physiological factors such as the body's reaction to the surgery.Moreover, blood pressure is manipulated and controlled, during and aftersurgery, using various medications. Often, these physiological factorsand the given medications can result in a situation of rapidly changingblood pressure requiring immediate blood pressure measurement, andcorrective action.

Because of changes in the patient's blood pressure, constant monitoringis important. The traditional method of measuring blood pressure is witha stethoscope, occlusive cuff and pressure manometer. However, thistechnique is slow, subjective in nature, requires the intervention of askilled clinician and does not provide timely readings frequentlyrequired in critical situations.

For these reasons, two methods of measuring blood pressure have beendeveloped: noninvasive, intermittent methods that use an automated cuffdevice such as an oscillometric cuff; and invasive, continuous(beat-to-beat) measurements that use a catheter.

The oscillometric cuff method typically requires 15 to 45 seconds toobtain a measurement, and should allow sufficient time for venousrecovery. Thus, at best there is typically 1/2 to 1 minute betweenupdated pressure measurements. This is an inordinately long amount oftime to wait for an updated pressure reading when fast actingmedications are administered. Also, too frequent cuff inflations overextended periods may result in ecehymosis and/or nerve damage in thearea underlying the cuff. The invasive method has inherent disadvantagesincluding risk of embolization, infection, bleeding and vessel walldamage.

To address the need for continuous, noninvasive blood pressuremeasurement, several systems were developed. One approach relies onblood pressure values in a patient's finger as indicative of thepatient's central blood pressure, as in the cases of Penaz, U.S. Pat.No. 4,869,261 and H. Shimazu, Vibration Techniques for IndirectMeasurement of Diastolic Arterial Pressure in Human Fingers, Med. andBiol. Eng. and Comp., vol. 27, no. 2, p. 130 (March 1989). Anothersystem uses two cuffs, one on each arm, to determine calibrationreadings and continuous readings respectively. Another system transformsa time sampled blood pressure waveform into the frequency domain anddetermines blood pressure based on deviations of the fundamentalfrequency. Kaspari, et al. U.S. patent application Ser. No. 08/177,448,filed Jan. 5, 1994 provides examples of these systems. An additionalclass of devices, represented by L. Djordjevich et al. WO 90/00029 (PCTApplication), uses electrical conductance to determine blood pressure.

A related area of interest was explored by perturbing the body tissue ofpatients. One class of experiments causes perturbations by inducingkinetic energy into the patient, specifically, by oscillating a bloodvessel. In the work of Seale, U.S. Pat. No. 4,646,754, an attempt isdescribed to measure blood pressure by sensing the input impedance of ablood vessel exposed to a low frequency vibration. In work by H. Hsu,U.S. Pat. No. 5,148,807, vibrations are used in a non-contact opticaltonometer. Several experiments measured the velocity of excitedperturbations in the blood and demonstrated a correlation betweenperturbation velocity and blood pressure. Such a correlation has alsobeen demonstrated between pressure and the velocity of the natural pulsewave. However, while these studies discuss the relationship betweenvelocity and pressure they do not propose a practical method ofmeasuring induced perturbations to determine blood pressure. Examples ofsuch studies are M. Landowne, Characteristics of Impact and Pulse WavePropagation in Brachial and Radial Arteries, J. Appl. Physiol., vol. 12,p. 91 (1958); J. Pruett, Measurement of Pulse-Wave Velocity Using aBeat-Sampling Technique, Annals of Biomedical Engineering, vol. 16, p.341 (1988); and M. Anliker, Dispersion and Attenuation of SmallArtificial Pressure Waves in the Canine Aorta, Circulation Research,vol. 23, p.539 (October 1968).

Known techniques for measuring propagation of pressure perturbations inarteries include Tolles, U.S. Pat. No. 3,095,872 and Salisbury, U.S.Pat. No. 3,090,377. Tolles employs two sensors to detect a perturbationwaveform and generate two sensor signals. The two sensor signals arecompared in a phase detector. The phase difference of the sensor signalsis displayed giving a signal that is capable of detecting changes inblood pressure, but which does not provide a calibrated blood pressureoutput. Salisbury similarly employs a sensor to detect a perturbationwaveform and generate a single sensor signal. The sensor signal iscompared against a reference signal. Based on the phase difference ofthe sensor signal, a universal formula is employed to determine thepatient's blood pressure. Since it has been shown, for example byLandowne, that the relationship between pressure and signal propagationvaries considerably from patient to patient, Salisbury's technique,based on a single formula, is not generally applicable.

OBJECTS AND SUMMARY OF THE INVENTION

The present invention describes an apparatus and method for measuringthe induced perturbation of a patient's body tissue to determine thepatient's blood pressure and other clinically important parameters.

An object of the present invention is to continuously determine apatient's blood pressure via a noninvasive sensor attached to thepatient.

A related object is to induce a perturbation into a patient's blood orblood vessel and to noninvasively measure the perturbation to determinethe patient's blood pressure.

A related object is to filter the noninvasive sensor signal intocomponents including a natural component, an induced component and anoise component, and to determine the patient's blood pressure from theinduced component.

A further related object is to determine a relationship between aproperty of an induced perturbation and a property of a physiologicalparameter.

A monitor for determining a patient's physiological parameter includes acalibration device configured to provide a calibration signalrepresentative of the patient's physiological parameter. An exciter ispositioned over a blood vessel of the patient for inducing a transmittedexciter waveform into the patient. A noninvasive sensor is positionedover the blood vessel, where the noninvasive sensor is configured tosense a hemoparameter and to generate a noninvasive sensor signalrepresentative of the hemoparameter containing a component of aphysiological parameter waveform and a component of a received exciterwaveform. In this context, a hemoparameter is defined as anyphysiological parameter related to vessel blood such as pressure, flow,volume, velocity, blood vessel wall motion, blood vessel wall positionand other related parameters. A processor is configured to determine arelationship between a property of the received exciter waveform and aproperty of the physiological parameter. The processor is connected toreceive the calibration signal and the noninvasive sensor signal, andthe processor is configured to process the calibration signal and thenoninvasive sensor signal to determine the physiological parameter. Inthe preferred embodiment, the physiological parameter measured is bloodpressure, however, the present invention can also be used to analyze andtrack other physiological parameters such as vascular wall compliance,strength of ventricular contractions, vascular resistance, fluid volume,cardiac output, myocardial contractility and other related parameters.

BRIEF DESCRIPTION OF THE FIGURES

Additions advantages of the invention will become apparent upon readingthe following detailed description and upon reference to the drawings,in which:

FIG. 1 depicts the present invention attached to a patient;

FIG. 2 depicts an exciter attached to a patient;

FIG. 3 depicts a noninvasive sensor attached to a patient;

FIG. 4a depicts a blood pressure waveform;

FIG. 4b depicts a blood pressure waveform with an exciter waveformsuperimposed thereon;

FIG. 5 depicts a schematic diagram of the present invention;

FIGS. 6a-b depict a processing flow chart according to one embodiment ofthe invention;

FIGS. 7a-c are graphical illustrations of the filter procedures of thepresent invention;

FIGS. 8a-c are graphical illustrations showing the relationships betweenthe exciter waveform and blood pressure;

FIGS. 9a&b depict a processing flow chart according to anotherembodiment of the invention;

FIGS. 10a&b depict a processing flow chart according to anotherembodiment of the invention; and,

FIG. 11 depicts an exciter and noninvasive sensor attached to a patient.

Glossary

P_(D) diastolic blood pressure

P_(D0) diastolic blood pressure at calibration

P_(S) systolic blood pressure

P_(p) pulse pressure

P_(w) exciter waveform pressure

V_(d) received exciter waveform

V_(w) signal exciter waveform

V_(n) noise waveform

V_(e) exciter sensor signal (transmitted exciter waveform)

V_(P) detected pulsatile voltage

Φw exciter signal phase

Φw_(D) exciter signal phase at diastole

Vel(t) exciter signal velocity

Vel_(D) exciter signal velocity at diastole

Vel_(D) exciter signal velocity at systole

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment concentrates on the physiological parameter ofblood pressure, however, many additional physiological parameters can bemeasured with the present invention including vascular wall compliance,ventricular contractions, vascular resistance, fluid volume, cardiacoutput, myocardial contractility and other related parameters. Thoseskilled in the art will appreciate that various changes andmodifications can be made to the preferred embodiment while remainingwithin the scope of the present invention. As used herein, the termcontinuous means that the physiological parameter of interest isdetermined over a period of time, such as during the course of surgery.The implementation of portions of the invention in a digital computer isperformed by sampling various input signals and performing the describedprocedures on a set of samples. Hence, a periodic determination of thephysiological parameter of interest is within the definition of the termcontinuous.

FIG. 1 illustrates the components and configuration of the preferredembodiment. Oscillometric cuff 110 is connected to processor 100 viawire 106, and cuff 110 is responsive to processor 100 during an initialcalibration step. Oscillometric cuff operation, which is known in theart, involves an automated procedure for obtaining a blood pressuresignal. The general procedure is given for clarity but is not crucial tothe invention.

First, an occlusive cuff is pressurized around the patient's upper armto abate the blood flow. Then, as the pressure is slowly reduced, atransducer senses when the blood flow begins and this pressure isrecorded as the systolic pressure. As the pressure is further reduced,the transducer similarly detects the pressure when full blood flow isrestored and this pressure is recorded as the diastolic pressure. Thesignals representing pressure are delivered, via wire 106, to processor100 for storage. An alternative blood pressure measurement techniquesuch as manual or automated sphygmomanometry using Korotkoff sounds or"return to flow" techniques, could also be used. A manual measurementcan be provided, for example, using a keypad. Whatever measurementtechnique is used, a calibration device provides a calibration signalrepresentative of the patient's physiological parameter. In thisrespect, the calibration device is broadly defined to include automatedor manual measurements.

FIG. 1 shows an exciter 202 attached to the patient's forearm above theradial artery. The exciter 202 is a device for inducing a perturbationof the patient's body tissue, and is controlled by the processor 100 viatube 107.

FIG. 2 shows a cross section of the exciter and its components. Theexciter 202 is an inflatable bag attached to the processor via air tube107. It is fixed in place near an accessible artery 220 by holddowndevice 204 which can be a buckle, adhesive strap or other device. Thereis also an exciter sensor 203 disposed within the exciter to generate areference signal indicative of the perturbation source waveform, and todeliver the signal to the processor via wire 108. This signal is used asa reference signal by the processor (explained below).

As mentioned above, processor 100 is attached to the exciter via tube107. The processor 100 controls the pressure in exciter 202 with atransducer and diaphragm. A transducer is a device that transforms anelectrical signal to physical movement, and a diaphragm is a flexiblematerial attached to the transducer for amplifying the movement. Anexample of this combination is a loudspeaker. The diaphragm forms partof an airtight enclosure connected to air tube 107 and an input toinitialize the pressure. It will be clear to one skilled in the art thatthe transducer and air tube 107 and exciter 202 can be miniaturized andcombined into a single exciter element capable of acting as a vibratingair filled bag connected to the processor by an electrical drive signalalone, in the case that a source of substantially constant pressure suchas a spring is included in the exciter, or by an electrical drive signaland connection to a source of substantially constant pressure for thebag.

In operation, the pressure is initially established via theinitialization input and then the pressure is varied by an electricalsignal delivered to the transducer; the diaphragm produces pressurevariations in the tube in response to the transducer movement. Theresult is that the processor, by delivering an oscillating electricalsignal to the transducer, causes oscillating exciter pressure. Theexciter responds by perturbing the patient's tissue and inducing atransmitted exciter waveform into the patient.

The perturbation excites the tissue 221 and blood vessel 220 below theexciter and causes the transmitted exciter waveform to radiate withinthe patient's body, at least a portion of which travels along the bloodfilled vessel. The excitation waveform can be sinusoidal, square,triangular, or of any suitable shape. Experiments conducted to determinea range of satisfactory perturbation frequencies found that the range of20-1000 Hz works well. It is anticipated that frequencies of lesser than20 Hz and greater than 1000 Hz will also work well, and it is intendedthat this specification cover all frequencies insofar as the presentinvention is novel.

FIG. 1 further shows a noninvasive sensor 210 placed at a distance fromthe exciter on the patient's wrist. The noninvasive sensor is connectedto the processor 100 via wire 109.

FIG. 3 shows a cut-away view of the noninvasive sensor 210 placed overthe same radial artery 220 as the exciter. The sensor 210 is fixed inplace near the artery 220 by holddown device 211 which can be a buckle,adhesive strap or other device. The holddown device 211 also includes abaffle 212 to reduce noise, where the baffle is a pneumatic bagpressurized to hold the sensor 210 at a constant pressure against thepatient, for example at a pressure of 10 mm Hg. Alternately, baffle 212can be any suitable device such as a spring or foam pad.

The noninvasive sensor 210 is responsive to at least one hemoparameterof the patient and generates a signal in response thereto. In thiscontext, a hemoparameter is defined as any physiological parameterrelated to vessel blood such as pressure, flow, volume, velocity, bloodvessel wall motion, blood vessel wall position and other relatedparameters. In the preferred embodiment a piezoelectric sensor is usedto sense arterial wall displacement, which is directly influenced byblood pressure.

As is shown, the sensor is positioned over the radial artery 220 and itis responsive to pressure variations therein; as the pressure increases,the piezoelectric material deforms and generates a signal correspondingto the deformation. The signal is delivered to the processor 100 viawire 109.

FIG. 1 also shows the processor 100 that has a control panel forcommunicating information with the user. A power switch 101 is forturning the unit on. A waveform output monitor 102 displays thecontinuous blood pressure waveform for medical personnel to see. Thiswaveform is scaled to the pressures determined by the processor, andoutput to the monitor. A digital display 103 informs the user of thecurrent blood pressure; there is a systolic over diastolic and meanpressure shown. A calibrate button 104 permits the user to calibrate theprocessor at any time, by pressing the button. The calibration display105 shows the user the blood pressure at the most recent calibration,and also the elapsed time since calibration. The processor maintains arecord of all transactions that occur during patient monitoringincluding calibration blood pressure, calibration times, continuousblood pressure and other parameters, and it is anticipated thatadditional information can be stored by the processor and displayed onthe control panel.

Turning to the noninvasive sensor signal, in addition to a naturalhemoparameter, the noninvasive sensor signal contains a componentindicative of the exciter waveform traveling through the patient.Although the exciter component is designed to be small in comparison tothe natural hemoparameter, it contains valuable information. Therefore,the processor is used to separate the exciter waveform from the naturalhemoparameter, and to quantify the respective components to determinethe patient's blood pressure.

FIG. 4a shows a natural blood pressure waveform where the minimumrepresents the diastolic pressure and the maximum represents thesystolic pressure. This waveform has a mean arterial pressure (MAP) thatis a convenient reference for purposes of determining the DC offset ofthe waveform. Example pressure values are 80 mm Hg diastolic and 120 mmHg systolic respectively with a MAP DC offset of 90 mm Hg.

FIG. 4b shows an operational illustration of the arterial waveform; anexciter waveform superimposed on a natural blood pressure waveform. Theexciter induces the exciter waveform into the arterial blood at a firstlocation and the exciter waveform becomes superimposed on the naturalwaveform. Since the exciter waveform is small compared to the patient'snatural waveform, the natural waveform dominates as shown in FIG. 4b. Asmentioned above, the noninvasive sensor signal contains informationregarding both the natural waveform and the exciter waveform. Theprocessor 100 is designed to separate the constituent components of thenoninvasive sensor signal to continuously determine the patient's bloodpressure, as is discussed below.

FIG. 5 depicts a schematic diagram of the preferred embodiment. There isan oscillometric cuff controller 121 for controlling the oscillometriccuff and determining the readings therefrom to generate a signalrepresenting the patient's blood pressure. There is an induced wavefrequency generator 131 coupled to a pressure transducer 133 thattransforms an electrical input to a pressure output. The transduceroutput is connected to the exciter 202 and controls the exciter'soscillations for inducing the exciter waveform into the patient'sarterial blood.

The output of the exciter sensor 203 is fed to a band pass filter 134.This filter 134 separates the high frequency signal responsive to thetransducer pressure and delivers the resulting signal to RMS meter 135and to lock-in amplifier 143 reference input. In the preferredembodiment, the RMS meter output is sampled at a rate of 200 samples persecond with a 14 bit resolution and delivered to computer 150. It isanticipated that the sampling rate and resolution can be varied withgood results.

The output of the noninvasive sensor is fed to a charge amplifier 140that delivers a resulting signal to a low pass filter 141 and a bandpass filter 142. These filters separate the noninvasive sensor signalinto two constituent components representing an uncalibrated naturalblood pressure wave and a received exciter waveform respectively. Thelow pass filter output is sampled at a rate of 200 samples per secondwith 14 bit resolution and delivered to computer 150, and the band passfilter output is delivered to the lock-in amplifier 143 signal input.

The lock-in amplifier 143 receives inputs from band pass filter 134 asreference and band pass filter 142 as signal, which are the excitersensor signal (transmitted exciter waveform) and noninvasive sensorexciter signal (received exciter waveform) respectively. The lock-inamplifier uses a technique known as phase sensitive detection to singleout the component of the noninvasive sensor exciter signal at a specificreference frequency and phase, which is that of the exciter sensorsignal. The amplifier 143 produces an internal, constant-amplitude sinewave that is the same frequency as the reference input and locked inphase with the reference input. This sine wave is then multiplied by thenoninvasive sensor exciter signal and low-pass filtered to yield asignal proportional to the amplitude of the noninvasive sensor signalmultiplied by the cosine of the phase difference between the noninvasiveexciter signal and the reference. This is known as the in-phase or realoutput.

The amplifier 143 also produces an internal reference sine wave that is90 degrees out-of-phase with the reference input. This sine wave ismultiplied by the received exciter signal and low-pass filtered to yielda signal proportional to the amplitude of the noninvasive sensor signalmultiplied by the sine of the phase difference between the noninvasivesensor exciter signal and the reference. This is known as quadrature orimaginary output. The amplifier 143 then provides the computer 150 withinformation regarding the real and imaginary components of the receivedexciter signal as referenced to the phase of the transmitted excitersignal. Alternately, the amplifier can provide components representingthe magnitude and phase of the received exciter signal. In the preferredembodiment, the amplifier output is sampled at a rate of 200 samples persecond with a 14 bit resolution. It is anticipated that the samplingrate and resolution can be varied with good results.

The computer 150 receives input from the oscillometric cuff controller121, RMS meter 135, low pass filter 141 and lock-in amplifier 150. Thecomputer 150 also receives input from the user interface panel 160 andis responsible for updating control panel display information. Thecomputer 150 executes procedures for further separating constituentcomponents from the noninvasive sensor signal and attenuating thenoninvasive sensor noise component as shown in FIG. 6.

While the processing system described in the embodiments involves theuse of a lock-in amplifier 143, it will be clear to those personsskilled in the art that similar results can be achieved by frequencydomain processing. For example, a Fourier transform can be performed onthe various signals to be analyzed, and processing in the frequencydomain can be further performed that is analogous to the describedprocessing by the lock-in amplifier in the time domain. The variousfiltering steps described above can be advantageously performed in thefrequency domain. Processing steps in the frequency domain areconsidered as falling within the general category of the analysis of thetransfer function between the exciter sensor waveform and thenoninvasive sensor waveform and are intended to be covered by theclaims. The variety of techniques that are used in the art for thecalculation of transfer functions are also applicable to this analysis.

PROCESS EXCITER WAVEFORM VELOCITY TO DETERMINE OFFSET SCALING ANDEXCITER WAVEFORM AMPLITUDE TO DETERMINE GAIN SCALING

FIG. 6 is a processing flowchart that represents the operation of theFIG. 5 computer 150. The operation begins at step 702 with the receiptof an initial calibration measurement; noninvasive sensor signal andexciter sensor signal. Step 704 chooses the blood pressure waveformsegment for pulse reference, which is important for continuity ofmeasurement from pulse to pulse and for consistency over periods of timebetween calibration measurements. In this embodiment, the diastolicpressure (low-point) is chosen for purposes of simplicity, but any pointof the waveform can be chosen such as the systolic pressure or meanarterial pressure (MAP). The choice of the segment will relate to the DCoffset discussed below.

Step 706 is a filter step where the noninvasive sensor (received)exciter waveform is separated into signal and noise components. Thenoise components may have many sources, one of which is a signal derivedfrom the exciter that travels to the noninvasive sensor by an alternatepath, other than that along the artery taken by the signal of interest.Examples include bones conducting the exciter waveform and the surfacetissue such as the skin conducting the exciter waveform. Additionalsources of noise result from patient movement. Examples includevoluntary patient motion as well as involuntary motion such as movementof the patient's limbs by a physician during surgery.

FIGS. 7a-c illustrate the principles of the received exciter signalfiltering. During a natural pulse, the received exciter waveform V_(d)is represented by a collection of points that are generated in thecomplex plane by the real and imaginary outputs of the lock-in amplifier143 which is monitoring the noninvasive sensor signal. FIG. 7arepresents the received exciter waveform V_(d) in the absence of noise.In the absence of noise, V_(d) is the same as vector V_(w) (t) which hasa magnitude and phase corresponding to the received exciter signal.During a pulse, the magnitude of V_(w) (t) remains constant, but theangle periodically oscillates from a first angle representing a lesserpressure to a second angle representing a greater pressure. Note that inthe absence of noise, the arc has a center at the origin.

FIG. 7b represents the received exciter waveform V_(d) in the presenceof noise, which is indicated by vector V_(n). Vector V_(d) has amagnitude and phase according to the noninvasive sensor exciter waveformplus noise. As can be seen in FIGS. 7b-c, vector V_(d) (t) defines acollection of points forming an arc having a common point V_(c)equidistant from each of the collection of points. The vector V_(w) (t)from V_(c) to the arc corresponds to the true magnitude and phase of thenoninvasive signal exciter waveform. The vector V_(n) represents noiseand, once identified, can be removed from the noninvasive sensorwaveform. The filter step removes the V_(n) noise component and passesthe V_(w) (t) signal exciter component on to step 708.

In the above discussion, it was assumed for illustrative purposes thatthe magnitude of V_(w) (t) remains constant over the time of a pulse. Insome cases the attenuation of the exciter waveform as it propagatesalong the artery is pressure dependent, and in those cases the magnitudeof V_(w) (t) can vary during the pulse in a way that is correlated topressure. Under such circumstances the shape of the figure traced out inthe complex plane by the vector V_(d) will deviate from a perfect circlesegment. A typical shape is that of a spiral with a form that can bepredicted theoretically. The functioning of this filter step under suchcircumstances is conceptually similar to that described above, exceptthat the elimination of the noise vector V_(n) must involve location ofthe origin of a spiral rather than of the center of a circle.

Step 708 determines if the pulse is valid. To do this, the processorchecks the constituent components of the noninvasive sensor signal toinsure that the components are within acceptable clinical norms of thepatient. For example, the processor can determine whether the new pulseis similar to the prior pulse, and if so, the new pulse is valid.

Step 720 processes the signal exciter waveform V_(w) (t) to determinethe DC offset. For convenience the diastole is used as the offset value,but any part of the waveform can be used. The processor determines theoffset when the vector V_(w) (t) reaches its lowest phase angle (i.e.,the maximum clockwise angle of FIG. 7a); this is the diastole phaseangle Φw(dias). A calibration diastolic measurement is stored by theprocessor at calibration as P_(D0). Also stored by the processor is arelationship denoting the relationship between the velocity of anexciter wave and blood pressure. This relationship is determined byreference to a sample of patients and is continuously updated byreference to the particular patient after each calibration measurement.FIGS. 8a-c are graphical illustrations showing clinically determinedrelationships between the exciter waveform and blood pressure. FIG. 8brepresents the relationship between phase and pressure at a frequency of150 Hz; other frequencies have relationships that are vertically offsetfrom the line shown. The pressure-velocity relationship represents thestorage of this graphical information either in a data table or by ananalytical equation.

Step 721 determines the predicted diastolic pressure from theinformation in Step 720. The processor continuously determines thechange in diastole from one pulse to the next by referencing theposition of the signal exciter vector V_(w) (t), at Φw(dias), withrespect to the stored pressure-velocity relationship. Moreover, thepressure-velocity relationship is continuously updated based oncalibration measurement information gained from past calibrations of thepatient.

A set of established relationships is used to develop and interpretinformation in the table and to relate the information to the sensorsignal components. First, a known relationship exists between bloodpressure and exciter waveform velocity. Also, at a given frequency manyother relationships are known: a relationship exists between velocityand wavelength, the greater the velocity the longer the wavelength; anda relationship exists between wavelength and phase, a change inwavelength will result in a proportional change in phase. Hence, arelationship exists between blood pressure and phase, and a change inblood pressure will result in a proportional change in phase. This isthe basis for the offset prediction.

With the stored calibration measurement plus the change in diastole, thenew DC offset diastolic pressure is predicted P_(D) (pred). Thisprediction is made based on the diastolic pressure at calibration P_(D0)plus the quotient of the phase difference between calibration Φw_(D0)and the present time Φw(dias) and the pressure-velocity relationshipstored in processor memory as rate of change of exciter waveform phaseto pressure d(Φw_(D))/dP. ##EQU1##

Step 722 displays the predicted diastolic pressure.

Step 730 determines the noninvasive sensor exciter waveform phase andvelocity. This determination is made based on the comparison of thenoninvasive sensor exciter waveform with the exciter sensor waveform.

Step 731 determines the noninvasive sensor exciter waveform amplitudefrom the noninvasive sensor signal.

Step 732 determines the exciter waveform pressure P_(w) by multiplyingthe exciter sensor waveform magnitude V_(e) by the ratio of thecalibrated exciter waveform pressure P_(w) (cal) to the calibratedexciter sensor waveform magnitude V_(e) (cal). ##EQU2## In situationswhere a significant pressure variation can be observed in theattenuation of the exciter waveform as it propagates from exciter todetector, an additional multiplicative pressure dependent correctionfactor must be included in equation 2.

Step 734 determines if the calibration values are still valid. Thisdetermination can be based on many factors including the time since thelast calibration, that the linearity of the pressure-velocityrelationship is outside of a reliable range, determination by medicalpersonnel that a new calibration is desired or other factors. As anexample of these factors, the preferred embodiment provides usersettable calibration times of 2, 5, 15, 30, 60 and 120 minutes, andcould easily provide more. Moreover, the curve upon which the pressureis determined is piecewise linear with some degree of overallnonlinearity. If the processor 100 determines that the data isunreliable because the linear region is exceeded, the processor willinitiate a calibration step. Finally, if the operator desires acalibration step, a button 104 is provided on the processor 100 forinitiating calibration manually.

Step 736 predicts a new pulse pressure P_(p) (pred) by multiplying theexciter waveform pressure P_(w) by the ratio of the detected pulsatilevoltage V_(p) to the detected exciter waveform magnitude V_(w). ##EQU3##This prediction uses the noninvasive sensor exciter waveform todetermine the pressure difference between the diastole and systole ofthe natural blood pressure waveform. For example, if a noninvasivesensor exciter magnitude V_(w) of 0.3 V relates to a pressure variationP_(w) of 1 mm Hg and the noninvasive sensor waveform V_(p) varies from-6 V to +6 V, then the noninvasive sensor waveform represents a pulsepressure excursion P_(p) (pred) of 40 mm Hg.

Step 760 predicts a new systolic pressure P(pred) by adding thepredicted diastolic P_(D) (pred) and pulse pressures P_(p) (pred).

    P.sub.s (pred)=P.sub.D (pred)+P.sub.p (pred)               (5)

In the above example if the diastole P_(D) (pred) is 80 mm Hg (DCoffset) and the pulse P_(p) (pred) represents a difference of 40 mm Hgthen the new systolic P_(s) (pred) is 120 mm Hg. Then the new systolicpressure is displayed.

For display purposes the values determined for P_(S) (pred) and P_(D)(pred) can be displayed numerically. Similarly, the output waveform fordisplay 102 can be displayed by scaling the noninvasive sensor naturalblood pressure waveform prior to output using gain and offset scalingfactors so that the output waveform has amplitude, P_(P) (pred), and DCoffset, P_(D) (pred), equal to those predicted in the above process. Thescaled output waveform signal can also be output to other instrumentssuch as monitors, computers, processors and displays to be used fordisplay, analysis or computational input.

Step 750 is taken when step 734 determines that the prior calibration isno longer reliable as described above. A calibration step activates theoscillometric cuff 201 and determines the patient's blood pressure, asdescribed above. The processor 100 uses the calibration measurements tostore updated pressure and waveform information relating to the DCoffset, blood pressure waveform and exciter waveform. The updatedvariables include calibration pulse pressure P_(p) (cal), calibrationexciter sensor waveform magnitude V_(e) (cal), diastolic pressureP_(D0), diastolic exciter waveform phase Φw_(D0), the rate of change ofexciter waveform phase to pressure d(Φw_(D))/dP and calibration exciterwaveform pressure P_(w) (cal). ##EQU4##

PROCESS EXCITER WAVEFORM VELOCITY TO DETERMINE OFFSET SCALING AND GAINSCALING

FIGS. 9a-b represent a modification to the previous embodiment. Theinitial processing steps 702, 704, 706, 708, 730 and 731 represented inthe flow chart of FIG. 9 are substantially similar to those described inthe previous embodiment depicted in FIG. 6. In step 730, exciterwaveform velocity Vel(t) and the actual phase delay of the exciterwaveform Φ(t) are related by the equation:

    Φ(t)=Φ.sub.0 -2πdf/Vel(t)                       (6)

where frequency f and distance d between exciter and noninvasive sensorare known. The constant Φ₀ is determined in advance either analyticallyor empirically, and is dependent on the details of the geometry of theapparatus.

Measurement of Φ(t) is generally made modulo 2π, and so the measuredphase Φ_(m) (t) is related to actual phase delay by the equation:

    Φ.sub.m (t)=Φ(t)+2nπ                            (7)

where n is an integer also known as the cycle-number, typically in therange of 0-10. While correct deduction of propagation velocity requiresa correct choice of n, a correct prediction of pressure using apressure-velocity relation does not, so long as the same value of n isused in determining Φ(t) and in determining the pressure-velocityrelationship. In such a case, velocity should be considered as apseudo-velocity rather than an actual measure of exciter waveformpropagation speed.

In step 730, therefore, use of the Φ(t) equations allows determinationof the velocity, or pseudo-velocity, Vel(t) as a function of time. Instep 801, the values of velocity at the systolic and diastolic points ofthe cardiac cycle are determined as Vel_(s) and Vel_(D). Thesecorrespond to the points of minimum and maximum phase delay or to thepoints of maximum and minimum amplitude of the naturally occurring bloodpressure wave detected by the noninvasive sensor. Use of thepressure-velocity relationship stored in the processor is then made totransform the values of velocity at systolic and diastolic points intime to values of pressure. In step 803 the diastolic pressure isdetermined using the equation:

    P.sub.D (pred)=P.sub.D0 +(Vel.sub.D -Vel.sub.D0)/(dVel/dP) (8)

Step 804 is performed to determine the predicted systolic pressureaccording to the relationship:

    P.sub.S (pred)=P.sub.D (pred)+(Vel.sub.S -Vel.sub.D)/(d.sub.Vel/dP)(9)

In this illustration the values of P_(S) and P_(D) are used to determinethe pressure waveform. Similarly, other pairs of values, such as meanpressure and pulse pressure can also be used, and appropriatepermutations of the predicted pressure equations are anticipated by thisdescription.

In step 805 the calculated pressures are displayed as numbers, with atypical display comprising display of mean, systolic and diastolicvalues of the pressure waveform in digital form, together with theobserved pulse rate. The values of P_(D) (pred) and P_(S) (pred) areused to determine appropriate gain and DC offset scaling parameters bywhich the naturally occurring blood pressure waveform detected by thenoninvasive sensor is scaled prior to output in step 806 as a timevarying waveform, shown as 102 in FIG. 1.

As in the embodiment depicted in FIG. 6, step 750 involves a calibrationstep initiated when step 734 determines that the prior calibration is nolonger reliable. During the performance of step 750 thepressure-velocity relationship is determined and stored in the processorin the form of a table or of an analytical relationship. During thisprocess, it may be desirable to stop the output portion of the processas shown in step 752 and display a different signal, such as a blankscreen, a dashed line display, a blinking display, a square wave, orsome other distinguishable signal of calibration such as an audibletone. This step is represented as step 808 in FIG. 9.

PROCESS EXCITER WAVEFORM VELOCITY TO DETERMINE OUTPUT BLOOD PRESSUREWAVEFORM

In both of the previous two embodiments, values of gain Pp(pred) andoffset P_(D) (pred) are determined and used to scale the noninvasivesensor natural blood pressure waveform to provide a time varying outputwaveform representative of the patient's blood pressure. In thisembodiment, the natural blood pressure waveform monitored by thenoninvasive sensor is not used in the determination of the output bloodpressure waveform. As in the previous embodiment, use is made of therelationship between velocity of the exciter waveform and the bloodpressure of the patient to determine the blood pressure. Rather thanmaking such a pressure determination only at the diastolic and systolicpoints of the cardiac cycle, exciter waveform velocity is measured manytimes during a cardiac cycle (typically 50-200 times per second) and theresultant determinations of pressure are used to construct the outputtime varying blood pressure waveform. This process is described belowwith reference to FIG. 10.

In this embodiment, the natural blood pressure waveform is not scaled.Therefore, there is no need to separate the data into pulse segments asin step 704 of FIG. 6. This feature greatly simplifies the computationaltask. An additional advantage of this technique is that all of theinformation used in the analysis process is encoded in the exciterwaveform, which is typically at a high frequency compared with that ofboth the natural blood pressure waveform and that of any artifactsignals introduced by patient motion or respiration. Since all of theselower frequency signals can be removed by electronic filtering, thistechnique is extremely immune to motion induced artifact and similarsources of interference that might otherwise introduce errors into themeasurement.

With the exception of this step, the initial processing steps 702, 706,731 and 730 are substantially similar to those of previously describedembodiments. The amplitude and phase of the exciter waveform determinedin step 731 are continuous functions of time. The exciter waveform phaseis converted to exciter waveform velocity as described previously, whichis also a continuous function of time.

Using a relationship between pressure and velocity, determined during orsubsequent to the initial calibration and periodically redetermined, thetime dependent velocity function Vel(t) is readily transformed to a timedependent pressure function P(t). This transformation is represented bystep 802. In a typical case, the pressure-velocity relationship might beas follows:

    Vel(t)=a+bP(t)                                             (10)

where the constants a and b were determined during step 750. In thatcase the velocity equation (10) can be used to perform thetransformation of step 802.

Following a variety of checking steps, described below, that ensure thetransformation used in 802 was correct, the minimum and maximum pointsof P(t) are determined for each cardiac cycle and displayed as P_(D)(pred) and P_(S) (pred) in step 805. Then, in step 806, the entire timedependent waveform is displayed as waveform 102.

DETERMINATION OF THE PRESSURE-VELOCITY RELATIONSHIP

In each of the embodiments described thus far, an important stepinvolves the conversion of a measured phase to a deduced exciterwaveform velocity, and conversion of that value to a pressure. In thecase of the flow chart of FIG. 6, this process is integral to thecalculation of the DC offset pressure P_(D0). In the case of theembodiment described in FIG. 9, this process is integral todetermination of P_(S) and P_(D). In the case of the embodimentdescribed in FIG. 10, the process is integral to the determination ofpressure at each point in time for which an output value is to bedisplayed as part of a "continuous" pressure waveform display.

The relationship between pressure and velocity is dependent on manyfactors including the elastic properties of the artery along which theexciter waveform travels. This relationship varies considerably betweenpatients, and must therefore be determined on a patient by patientbasis, although a starting relationship derived from a pool of patientscan be used. This determination occurs during step 750 in each of theembodiments described in FIGS. 6, 9, and 10, and the relationship isstored in the processor in either a tabular form, or as an analyticalrelationship. In step 734 in FIGS. 6, 9 and 10, a variety of parametersare examined to determine whether the system calibration continues to beacceptable. As part of that process, it is determined whether theexisting pressure-velocity relationship continues to be valid. If not, arecalibration can be initiated.

MULTIPLE PERTURBATIONS

For each of the different embodiments described hereto, an additionalembodiment is described using multiple perturbation waveforms. All thefeatures and advantages of the prior embodiments are applicable to theseembodiments.

In the case of each of the previously described embodiments anembodiment is described in which the apparatus further induces a secondexciter waveform into the arterial blood. An example second exciterwaveform is one that has a frequency different from that of the firstexciter waveform. It is noted that although the discussion of the secondembodiment concentrates on a second exciter wave, any number of two ormore exciter waves can be used to determine the perturbation velocitymeasurement.

In operation, processor 100 generates two exciter waveforms andcommunicates the waveforms to the exciter 202 via air tube 107. Theexciter 202 responds by inducing both exciter waveforms into thepatient. Noninvasive sensor 210 generates a signal responsive to ahemoparameter and transmits the signal to the processor 100 via wire109.

The processor filters the noninvasive sensor signal into components ofthe natural waveform, a first exciter waveform, a second exciterwaveform and noise. The processor determines the phase relationship ofthe first exciter waveform to a first reference input and determined thephase relationship of the second exciter waveform to a second referenceinput.

Once the processor has determined the phase of the exciter waveforms,the processor then generates a plurality of points, the slope of whichrelates to the velocity of the exciter waveform. This is shown in FIG.8c, where the slope of the line is -2πd/Vel, and where d is distance andVel is velocity. Since the distance is fixed and the slope is related toblood pressure, and since the slope changes based on changes in bloodpressure, the velocity of the exciter waveform is determined.

The technique described above yields a measurement of the groupvelocity. In contrast, the techniques described in previous embodimentsresult in the measurement: of a phase velocity or of a pseudo-phasevelocity in the case that the value of n of the phase equation (7) cannot be uniquely determined. In a dispersive system these values need notalways agree. However, phase, group and pseudo-velocity aremonotonically varying functions of pressure. Thus, a measurement of anyone of the three is a basis for a pressure prediction, so long as theappropriate pressure-velocity relationship is used.

An additional benefit of the use of multiple frequency perturbations isthat it allows the unique determination of the value of n in the phasemeasurement equation described above. This allows the use of actualphase velocity, rather than of the pseudo-velocity described earlier inthe multi-perturbation analogues of the embodiments depicted in FIGS. 6,9 and 10.

Once the velocity is determined, a prediction of blood pressure is madeaccording to FIG. 8a, showing the relationship of velocity to pressure.Thus, it is possible to determine the blood pressure with few, or zero,calibrations.

Another embodiment is depicted in FIG. 11 showing a cross section of anexciter 202 and noninvasive sensor 210 at the same position above theblood vessel 220. The proximate location of the exciter and the sensorpermits measurement of the blood vessel's response to the perturbations.In this embodiment, the noninvasive sensor is responsive to ahemoparameter such as blood flow or blood volume. These parameters canbe measured with a sensor such as a photoplethysmograph. Detectedchanges in the blood vessel due to the natural pulsatile pressure arecalibrated using external exciter pressure oscillations and comparedagainst the sensor signal by the processor.

VARIATIONS ON THE DISCLOSED EMBODIMENTS

Additional embodiments include an embodiment in which two or moredetectors are positioned along the artery at different distances from asingle exciter, and an embodiment in which two or more exciters arepositioned along the artery at different. distances from one or moredetectors. In each of these embodiments, the information. obtained fromeach exciter detector pair can be analyzed independently. The multiplyredundant measurements of pressure that result can be combined toprovide a single pressure determination that may be both more accurateand more immune from noise, motion artifact and other potential errorsources. Similar redundancy can be achieved in the embodiments that usemultiple exciter waveforms by analyzing the results at each frequencyindependently and combining the results to provide enhanced robustness.

In addition, any combination of more than two elements (e.g. twoexciters and one detector, two detectors and one exciter, one exciterand three detectors) allows the value of n in the phase equation (7) tobe uniquely determined so long as the spacing of two of the elements issufficiently small to be less than a wavelength of the propagatingperturbation. Since the possible range of perturbation wavelengths at agiven-pressure can be determined from a pool of patients, selection ofthe appropriate spacing is straightforward and can be incorporated intothe geometrical design of the device.

CONCLUSION

A close relationship between physiological parameters and hemoparameterssupplies valuable information used in the present invention. Theperturbation of body tissue and sensing the perturbation also suppliesvaluable information used in the present invention. Although thepreferred embodiment concentrates on blood pressure, the presentinvention can also be used to analyze and track other physiologicalparameters such as vascular wall compliance, changes in the strength ofventricular contractions, changes in vascular resistance, changes influid volume, changes in cardiac output, myocardial contractility andother related parameters.

Calibration signals for the present invention can be obtained from avariety of sources including a catheter, manual determination, or othersimilar method.

The DC offset for the physiological parameter waveform can be obtainedin a variety of ways for use with the present invention.

The exciter of the preferred embodiment uses air, but any suitable fluidcan be used. Moreover, various exciter techniques can be used forinducing an exciter waveform into the patient such as an acousticexciter, an electromagnetic exciter and an electromechanical exciter(e.g. piezoelectric device).

Various noninvasive sensors have been developed for sensinghemoparameters. These sensor types include piezoelectric,piezoresistive, impedance plethysmograph, photoplethysmograph, varioustypes of strain gages, air cuffs, tonometry, conductivity, resistivityand other devices. The present invention can use any sensor thatprovides a waveform related to the hemoparameter of interest.

Having disclosed exemplary embodiments and the best mode, modificationsand variations may be made to the disclosed embodiments while remainingwithin the subject and spirit of the invention as defined by thefollowing claims.

What is claimed is:
 1. A monitor for determining a physiologicalparameter of a patient comprising:a calibration device configured toprovide a calibration signal representative of one of the patient'sphysiological parameters; an exciter adapted to be positioned over ablood vessel of the patient and configured to induce a transmittedexciter waveform into the patient; a noninvasive sensor adapted to bepositioned over said blood vessel and configured to sense ahemoparameter and to generate a noninvasive sensor signal representativeof said hemoparameter containing a component of a received exciterwaveform; a processor configured to determine a relationship between aproperty of said received exciter waveform and a property of saidphysiological parameter; wherein said processor includes a filterconfigured to separate a signal exciter waveform component of saidnoninvasive sensor signal from at least one other component of saidnoninvasive sensor signal; and wherein said processor is connected toreceive said calibration signal and said noninvasive sensor signal andis configured to determine said physiological parameter based at leastin part on said calibration signal, said signal exciter waveformcomponent, and said relationship.
 2. A monitor for determining aphysiological parameter of a patient comprising:a calibration deviceconfigured to provide a calibration signal representative of one of thepatient's physiological parameters; an exciter adapted to be positionedover a blood vessel of the patient and configured to induce atransmitted exciter waveform into the patient; a noninvasive sensoradapted to be positioned over said blood vessel and configured to sensea hemoparameter and to generate a noninvasive sensor signalrepresentative of said hemoparameter containing a component of areceived exciter waveform; a processor configured to determine arelationship between a property of said received exciter waveform and aproperty of said physiological parameter; wherein said processorincludes a filter configured to separate a component of said noninvasivesensor signal having a phase that varies with blood pressure from atleast one other component of said noninvasive sensor signal having aphase that does not so vary; and wherein said processor is connected toreceive said calibration signal and said noninvasive sensor signal andis configured to determine said physiological parameter based at leastin part on said calibration signal, said component having a phase thatvaries with blood pressure, and said relationship.
 3. The monitor ofclaim 2, wherein:said processor includes a filter configured todetermine an are representing time varying positions of said receivedexciter waveform, to determine a center point of said are and todetermine a noise vector from an origin to said center point; and saidprocessor is configured to determine an arc vector from said centerpoint to said time varying positions, where said arc vector has an arcvector angle that moves from a first angle to a second angle over time;and wherein said processor is configured to process said arc vectorangle to determine said physiological parameter.
 4. The monitor of oneof claims 1, 2 or 3, wherein:said processor is further configured todetermine a relationship between a component of said received exciterwaveform and an amplitude and value of said physiological parameter. 5.The monitor of one of claims 1, 2 or 3, wherein:said processor isfurther configured to determine a relationship between an amplitude andphase, of a component of said received exciter waveform and an amplitudeand value of said physiological parameter.
 6. A monitor for determininga physiological parameter of a patient, comprising:a calibration deviceconfigured to provide a calibration signal representative of one of thepatient's physiological parameters; an exciter adapted to be positionedover a blood vessel of the patient and configured to induce atransmitted exciter waveform into the patient; a noninvasive sensoradapted to be positioned over said blood vessel and configured to sensea hemoparameter and to generate a noninvasive sensor signalrepresentative of said hemoparameter containing a component of areceived exciter waveform; a processor configured to determine arelationship between a property of said received exciter waveform and aproperty of said physiological parameter; and wherein said processor isconnected to receive said calibration signal and said noninvasive sensorsignal and is configured to determine said physiological parameter basedat least in part on said calibration signal, said noninvasive sensorsignal and said relationship; wherein said exciter is further configuredto induce a second transmitted exciter waveform into the patient; andwherein said processor includes a filter configured to separate fromsaid noninvasive sensor signal a component of one of the groupconsisting of said physiological parameter waveform, said receivedexciter waveform, a second received exciter waveform, a signal exciterwaveform, second signal exciter waveform and a noise waveform.
 7. Themonitor of one of claims 1, 2, 3 or 6, wherein:said processor isresponsive to said noninvasive sensor signal, and further configured todetermine the validity of said calibration signal and to initiate acalibration when said calibration signal is not valid.
 8. The monitor ofone of claims 1, 2, 3 or 6, wherein:said processor is further configuredto scale said physiological parameter waveform based on the relationshipbetween a property of said received exciter waveform and a property ofsaid physiological parameter and to generate a scaled physiologicalparameter waveform signal.
 9. A processor for determining aphysiological parameter of a patient with an apparatus having acalibration device configured to provide a calibration signalrepresentative of one of the patient's physiological parameters, anexciter adapted to be positioned over a blood vessel of the patient andconfigured to induce a transmitted exciter waveform into the patient,and a noninvasive sensor adapted to be positioned over said blood vesseland configured to sense a hemoparameter and to generate a noninvasivesensor signal representative of said hemoparameter, said processorcomprising:a first input configured to receive said calibration signal;a second input configured to receive said noninvasive sensor signal; afilter configured to from said noninvasive sensor signal a componentrepresenting a received exciter waveform; a relationship routineconfigured to determine a relationship between a property of saidreceived exciter waveform and a property of said physiologicalparameter; wherein said filter is configured to separate a component ofsaid noninvasive sensor signal having a phase that varies with bloodpressure from at least one other component of said noninvasive sensorsignal having a phase that does not so vary; and a determination routineto determine said physiological parameter based at least in part on saidcalibration signal, said component having a phase that varies with bloodpressure, and said relationship.
 10. The processor of claim 9,wherein:said filter is configured to determine an arc representing timevarying positions of said received exciter waveform, to determine acenter point of said arc and to determine a noise vector from an originto said center point; and said filter is configured to determine an arcvector from said center point to said time varying positions, where saidarc vector has an arc vector angle that moves from a first angle to asecond angle over time; and wherein said determination routine isconfigured to process said are vector angle to determine saidphysiological parameter.
 11. The processor of one of claims 9 or 10,wherein:said determination routine is further configured to compare aphase relationship between said transmitted exciter waveform and acomponent of said noninvasive sensor signal to determine saidphysiological parameter.
 12. The processor of one of claims 9 or 10wherein:said filter is further configured to separate from saidnoninvasive sensor signal a component representing a second receivedexciter waveform.
 13. The processor of one of claims 9 or 10,wherein:said determination routine is further configured to compare aphase relationship between said transmitted exciter waveform and acomponent of said noninvasive sensor signal, and to compare a phaserelationship between a second transmitted exciter waveform and acomponent of said noninvasive sensor signal to determine saidphysiological parameter.
 14. A method for determining a physiologicalparameter of a patient comprising:providing a calibration signalrepresentative of one of the patient's physiological parameters andstoring the calibration signal; inducing a transmitted exciter waveforminto the patient; noninvasively sensing a hemoparameter and generating anoninvasive sensor signal representative of said hemoparametercontaining a component of a received exciter waveform; and processingsaid noninvasive sensor signal including the steps of:(a) determining arelationship between a property of said received exciter waveform and aproperty of said physiological parameter; (b) separating a signalexciter waveform component of said noninvasive sensor signal from atleast one other component of said noninvasive sensor signal; and (c)determining said physiological parameter based at least in part on saidcalibration signal, said signal exciter waveform component, and saidrelationship.
 15. A method for determining a physiological parameter ofa patient comprising:providing a calibration signal representative ofone of the patient's physiological parameters and storing thecalibration signal; inducing a transmitted exciter waveform into thepatient; noninvasively sensing a hemoparameter and generating anoninvasive sensor signal representative of said hemoparametercontaining a component of a received exciter waveform; and processingsaid noninvasive sensor signal including the steps of:(a) determining arelationship between a property of said received exciter waveform and aproperty of said physiological parameter; (b) separating a signalexciter waveform a component of said noninvasive sensor signal having aphase that varies with blood pressure from at least one other componentof said noninvasive sensor signal having a phase that does not so vary;and (c) determining said physiological parameter based at least in parton said calibration signal, said component having a phase that varieswith blood pressure, and said relationship.
 16. The method of claim 15,wherein:said processing step includes a filtering step of determining anarc representing time varying positions of said received exciterwaveform, determining a center point of said arc and determining a noisevector from an origin to said center point; and said processing stepincludes a filtering step of determining an arc vector from said centerpoint to said time varying positions, where said arc vector has an arcvector angle that moves from a first angle to a second angle over time.17. The method of one of claims 14, 15 or 16, wherein:said processingstep includes determining a relationship between a component of saidreceived exciter waveform and an amplitude and value of saidphysiological parameter.
 18. The method of one of claims 14, 15 or 16,wherein:said processing step includes determining a relationship betweenan amplitude and phase of a component of said received exciter waveformand an amplitude and value of said physiological parameter.
 19. A ofdetermining a physiological parameter of a patient, comprising the stepsof:providing a calibration signal representative of one of the patient'sphysiological parameters and storing the calibration signal; inducing atransmitted exciter waveform into the patient; noninvasively sensing ahemoparameter and generating a noninvasive sensor signal representativeof said hemoparameter containing a component of a received exciterwaveform; processing said noninvasive sensor signal including the stepsof:(a) determining a relationship between a property of said receivedexciter waveform and a property of said physiological parameter; and (b)determining said physiological parameter based at least in part on saidcalibration signal, said noninvasive sensor signal and saidrelationship; inducing a second transmitted exciter waveform into thepatient; and wherein said processing step includes a filtering step ofseparating from said noninvasive sensor signal a component of one of thegroup consisting of said physiological parameter waveform, said receivedexciter waveform, a second received exciter waveform, a signal exciterwaveform, a second signal exciter waveform and a noise waveform.
 20. Themethod of one of claims 14, 15, 16 or 19, wherein:said processing stepincludes determining the validity of said calibration signal andinitiating said step of providing a calibration signal when saidcalibration signal is not valid.
 21. The method of one of claims 14, 15,16 or 19, wherein:said processing step includes scaling saidphysiological parameter waveform based on the relationship between aproperty of said received exciter waveform and a property of saidphysiological parameter and generating a scaled physiological parameterwaveform signal.
 22. A monitor for determining a patient's bloodpressure comprising:an inflatable cuff adapted to be positioned on anextremity of the patient and configured to provide a calibration signalrepresentative of one of the patient's physiological parameters; anexciter adapted to be positioned over a blood vessel of the patient andconfigured to induce a transmitted exciter waveform into the patient; anoninvasive sensor adapted to be positioned over said blood vessel at adistance from said exciter and configured to sense a hemoparameter andto generate a noninvasive sensor signal representative of saidhemoparameter containing a component of a received exciter waveform; aprocessor configured to determine a relationship between a property ofsaid received exciter waveform and a property of said physiologicalparameter; wherein said processor is connected to receive saidcalibration signal and said noninvasive sensor signal; wherein saidprocessor includes a filter configured to separate a component of saidnoninvasive sensor signal having a phase that varies with blood pressurefrom at least one other component of said noninvasive sensor signalhaving a phase that does not so vary; and wherein said processor isconfigured to determine said blood pressure based at least in part onsaid calibration signal, said component having a phase that varies withblood pressure, and said relationship.
 23. The monitor of claim 22,further comprising:an exciter sensor adapted to be positioned near saidexciter and configured to sense said transmitted exciter waveform and togenerate an exciter sensor signal representative of said transmittedexciter waveform; and wherein said processor is further configured tocompare the phase relationship of said transmitted exciter sensor signaland said received exciter waveform to determine said blood pressure. 24.A method of obtaining data of blood pressure of a patient,comprising:noninvasively inducing into an artery of the patient arepetitive pressure wave; noninvasively monitoring a characteristic ofthe repetitive wave upon modification by the artery; determining arelationship between magnitudes of the monitored wave characteristic andblood pressure; using the monitored wave characteristic and saidrelationship in a manner to provide the blood pressure of the patient;and noninvasively monitoring relative values of the blood pressure inthe artery of the patient, and wherein using the monitored wavecharacteristic and said relationship includes scaling the monitoredrelative values of the blood pressure by the monitored wavecharacteristic and said relationship in a manner to provide absolutevalues of said blood pressure.
 25. The method of claim 24, whereinmonitoring the wave characteristic and monitoring the relative bloodpressure values include use of a single transducer having an electricalsignal output that is separated into components of the repetitivepressure wave and relative blood pressure by filtering.
 26. A method ofobtaining data of blood pressure of a patient, comprising:noninvasivelyinducing into an artery of the patient a repetitive wave uponmodification by the artery; determining a relationship betweenmagnitudes of the monitored wave characteristic and blood pressure;using the monitored wave characteristic and said relationship in amanner to provide the blood pressure of the patient; and wherein usingthe monitored wave characteristic and said relationship includesprocessing the monitored characteristic of the pressure wave aftermodification by the artery in a manner to separate a component thatvaries with a period of the blood pressure from other, components thatdo not so vary, thereby to filter out a desired component of themonitored characteristic.
 27. The method of claim 26, wherein thenoninvasive monitoring of a characteristic of the repetitive waveincludes measuring the characteristic between two spaced apart locationsalong a length of the artery.
 28. The method of claim 27 wherein thecharacteristic being measured includes a relative phase of said pressurewave between said two spaced apart locations.
 29. The method of one ofclaims 24, 25, 26 or 27, wherein determining the relationship betweenmagnitudes of said wave characteristic and values of blood pressure isaccomplished on the patient.
 30. The method of one of claims 24, 25 and27, wherein using the monitored wave characteristic and saidrelationship includes processing the monitored characteristic of thepressure wave after modification by the artery in a manner to separate acomponent that varies with a period of the blood pressure from othercomponents that do not so vary, thereby to filter out a desiredcomponent of the monitored characteristic.
 31. The method of one ofclaims 24, 25, 26, 27 or 28, which additionally comprises displaying thevalues of the blood pressure of the patient as a curve.
 32. The methodof one of claims 24, 25 or 26, wherein the noninvasive monitoring of acharacteristic of the repetitive wave includes measuring thecharacteristic between two spaced apart locations along a length of theartery.
 33. The method of one of claims 24, 25 or 26 wherein thenoninvasive monitoring of a characteristic of the repetitive waveincludes measuring the characteristic between two spaced apart locationsalong a length of the artery, and the characteristic being measuredincludes a relative phase of said pressure wave at said two spaced apartlocations.
 34. A method of obtaining data of blood pressure of apatient, comprising:noninvasively inducing into an artery of the patienta repetitive pressure wave, noninvasively monitoring a characteristic ofthe pressure wave between two spaced apart locations along a length ofthe artery, processing the monitored characteristic of the pressure waveby separating a component that varies with a period of the bloodpressure from other components that do not so vary, thereby to filterout a desired component of the monitored characteristic that is relatedto blood pressure, and determining the blood pressure from the filteredcomponent.
 35. The method of claim 34 wherein the monitoredcharacteristic includes a relative phase of said pressure wave betweensaid two spaced apart locations.
 36. The method of claims 34 or 35,which additionally comprises displaying the determined blood pressure ofthe patient as a curve.
 37. A monitor for determining a physiologicalparameter of a patient comprising:an exciter adapted to be positionedover a blood vessel of the patient and configured to induce atransmitted exciter waveform into the patient; a noninvasive sensoradapted to be positioned over said blood vessel and configured to sensea hemoparameter and to generate a noninvasive sensor signalrepresentative of said hemoparameter containing a received exciterwaveform component and a physiological waveform component; a processorconfigured to utilize a relationship between a property of said receivedexciter waveform component and a property of said physiologicalparameter; wherein said processor is configured to scale saidnoninvasive sensor signal including said physiological waveformcomponent by use of said relationship to generate a scaled waveform; andwherein said processor is connected to receive said sensor signal and isconfigured to determine said physiological parameter based at least inpart on said scaled waveform.
 38. A monitor for determining aphysiological parameter of a patient comprising:an exciter adapted to bepositioned over a blood vessel of the patient and configured to induce atransmitted exciter waveform into the patient; a noninvasive sensoradapted to be positioned over said blood vessel and configured to sensea hemoparameter and to generate a noninvasive sensor signalrepresentative of said hemoparameter containing a received exciterwaveform component and a physiological waveform component; a processorconfigured to utilize a relationship between a property of said receivedexciter waveform component and a property of said physiologicalparameter; wherein said processor is connected to receive said sensorsignal and is configured to determine said physiological parameter basedat least in part on said sensor signal and said relationship; and meansin addition to said sensor for noninvasively monitoring relative valuesof the physiological parameter of the patient, and wherein saidprocessor is additionally configured for scaling the monitored relativevalues of the physiological parameter by the sensor signal and saidrelationship in a manner to provide absolute values of saidphysiological parameter.
 39. A monitor for determining a physiologicalparameter of a patient comprising:an exciter adapted to be positionedover a blood vessel of the patient and configured to induce transmittedexciter waveform into the patient; a noninvasive sensor adapted to bepositioned over said blood vessel and configured to sense ahemoparameter and to generate a noninvasive sensor signal representativeof said hemoparameter containing a component of a received exciterwaveform; a processor configured to utilize a relationship between aproperty of said received exciter waveform and a property of saidphysiological parameter; wherein said processor is connected to receivesaid sensor signal and is configured to determine said physiologicalparameter based at least in part on said sensor signal and saidrelationship; and wherein said processor is additionally configured forprocessing the sensor signal in a manner to separate a component thatvaries with a period of blood pressure variations in the artery fromother components that do not so vary, thereby to filter out a desiredcomponent of the sensor signal.
 40. The monitor according to claim 39,additionally comprising means coupled with said processor for displayingthe values of the physiological parameter of the patient as a curve. 41.The monitor of one of claims 37, 38, 39 or 40 wherein the physiologicalparameter being monitored includes blood pressure.
 42. A method fordetermining a physiological parameter of a patientcomprising:noninvasively positioning over a blood vessel of the patientan exciter that induces an exciter waveform into the blood vessel;noninvasively positioning a sensor over the blood vessel of the patientat a location spaced a distance apart from the exciter along the bloodvessel in order to detect a sensor signal of the exciter waveform atsaid spaced apart location that contains a component representative of ahemoparameter of the patient; providing a relationship between aproperty of said sensor signal and a property of said physiologicalparameter; separating a component of said noninvasive sensor signalhaving a phase that varies with blood pressure from at least one othercomponent of said noninvasive sensor signal having a phase that does notso vary; and determining the physiological parameter from at least saidcomponent having a phase that varies with blood pressure, and saidrelationship.
 43. The method of claim 42 wherein said step ofdetermining the physiological parameter includes the step of measuring aphase of the sensor signal relative to that of the waveform induced intothe blood vessel by the exciter.
 44. The method of one of claims 42, or43, wherein the physiological parameter of the patient being monitoredincludes blood pressure.